Dictation system



Oct. 21, 1958 TAYLOR ETAL 2,857,475

DICTATION SYSTEM Original Filed Oct. 6, 1951 3 Sheets-Sheet 1 II II II VI 252 a a II l AMPLIFIER I64 236 32 14 ASSEMBLY L 8 230i I -J #54 ,1958D. E. TAYLOR El'AL 2,857g475 DICTATION SYSTEM Original Filed Oct. 6,1951 s Sheeis-Sheet 2 SUPPZY +SUPPLYE CLUTCH MAHK NVE TO 5 l) {I a [or22 0? R.Jo es ATTOR S Oct. 21, 1958 D. E. TAYLOR ETAL DICTAT-ION SYSTEM'3 Sheets-Sheet 3 Original Filed Oct. 6, 1951 $35? d B. Jones IN DougiasM m GAO:

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United States Patent DICTATION SYSTEM Douglas E. Taylor, Westport, andLloyd R. Jones, Stepney Depot, Conn., assignors to DictaphoneCorporation, Bridgeport, Conn., a corporation of New York Continuationof application Serial No. 250,122, October 6, 1951. This applicationMarch 18, 1957, Serial N0. 646,671

28 Claims. (Cl. 179100.1)

This application is a continuation of our copending application SerialNo. 250,122, filed October 6, 1951, now abandoned.

This invention relates to dictating equipment and more particularly tooffice-type dictating systems wherein several dictator stations areconnected to remotely-positioned central sound recording apparatus. Forexample, each of several associated oflices may be equipped with amicrophone, a receiver, and the necessary controls and signalindicators, and a single central recording apparatus may be used torecord the dictation from any of the ofiices.

In systems such as this, wherein the recording apparatus is positionedremotely from the person dictating and wherein a single sound recordingmachine is to be used by a number of persons each at a separate station,it is necessary to provide at the central station remotelyoperablecontrol means so that the dictator can operate the recording machine. Atthe same time it is necessary to prevent confusion or interferencebetween the dictator station that is in use and the other stations. Thatis, when one of the dictator stations is in use and controlling therecording apparatus, the other stations are prevented from recording andfrom interfering with the control of the recording apparatus.

Several systems incorporating remotely-controlled dictating machineshave been proposed, but in general they have utilized complex circuitarrangements. Such complicated systems are not useful commerciallybecause of this high initial cost and because of the great skillrequired for proper servicing and maintenance of the apparatus.

In accordance with the present invention, a highly reliable andrelatively simple and inexpensive system is provided that performs thedesired functions and which is easily installed and maintained. In theembodiment of the invention to be described in more detail later, eachdictator station is connected to the remotely-positioned sound recordingapparatus by a six wire cable and all of the dictating stations areconnected in parallel so that in most instances a single six wire cableextends from the central recording apparatus to each of the ofiices withrelatively short branch wires extending between the main cable and thedictator stations.

The system is arranged so that when the central recording apparatus isnot in use, its control can be taken over by any one of the dictatorstations and once this control has been acquired it cannot beinterrupted or interfered with from any of the other dictator stations,nor can a person listen in on the dictated material from anotherstation.

The person dictating is able to control the recording apparatus asconveniently as if the dictating machine were positioned adjacent him,and a separate control button or switch is provided for each function sothat it is unnecessary for the dictator to operate two control buttonsor switches simultaneously to produce a third function. However, twocontrol functions are combined .in the electrical circuits to produce athird function, thus reducing the number of interconnecting leads;electrical 2 p interlocks being provided to prevent interference betweenthe separate control circuits.

Suitable indications and signals are provided to apprise the persondictating of the condition ofthe recording apparatus. Thus, a signallight is provided at each dictator station to indicate that therecording apparatus is not in condition for use, as when a new record isneeded, or that the system is being operated from another dictatorstation. the record is approaching, an audible warning signal: isprovided in the receiver to warn the person who is dictating that only alimited amount of recording time remains. This warning signal is sofaintly audible that it does not interfere with normal dictation. Whenthe entire record has been used, a much louder audible signal isprovided and the recording apparatus is switched off automatically.

These and other aspects, objects, and advantages of the presentinvention will be in part pointed out in and in part apparent from thefollowing description of a preferred embodiment of the inventionconsidered together with the accompanying drawings, in which:

Figure 1 represents diagrammatically a dictation system showing twodictator stations and the central recording and control apparatus;

Figure 2 shows schematically the portion of the circuit of the apparatuspositioned at each of the dictator stations;

Figure 3 shows schematically the control and interlock circuits of acentral control unit; and

Figure 4 shows diagrammatically and schematically the recordingapparatus. and the associated circuits.

As shown in Figure 1, a desk-type telephone, generally indicated at 2,is positioned on a desk in an oflice, diagrammatically represented at 4.This telephone 2 is connected through a relay control unit, generallyindicated at 6, and a cable 8 to remotely-positioned recording apparatuscomprising a control unit, generally indicated at 12, and a dictatingmachine, generally indicated at 14.

Another telephone 2 and relay unit 6 are illustrated diagrammatically inan oflice 16 and are also connected to the remote dictating apparatus bymeans of the cable 8.

The representation of Figure l is intended to be diagrammatic and asmany telephone units as desired may be connected to the cable 8.However, in most applications, it is not desirable to connect more thansix to ten telephone units to a single recording apparatus.

When a person in ofhce 4 wishes to dictate, he lifts the telephone handset 18 and presses a clutch-operating thumb switch (not shown in Figurel) which is mounted on the hand set 18. A correction marker switch 20 isprovided on the base of the telephone 2 so that the person dictating cancause indications, for the guidance of the secretary during thetranscription, to be produced on the top sheeet of a pad 22 of indicatorslips on the dictating machine 14. A play-back switch 24 is alsoprovided on the base of the telephone 2 so that the person dictating canreproduce the most recently recorded material.

if the hand set in the office 4 has been lifted from its receiver, asignal light 26 in the base of this instrument lights and correspondingsignal lights in each of the other telephone sets are illuminated sothat anyone else wishing to dictate will be informed that the dictatingapparatus is already in use.

A privacy system is arranged so that when one of the telephone sets isbeing used for dictation, the lifting of any other of the hand sets willnot interfere with the person using the dictating apparatus and so thatit is impossible for any other person to listen in on the dietation. Theelectrical circuits of te dictating system are illustrateddiagrammatically in Figures 2, 3, and 4 which form a single compositecircuit by interconnection of the 2,857,475 Patented Oct. 21, 1958 Whenthe end of the recording area of 3 leads bearing corresponding numbersin the various figures.

When the dictating apparatus is not in use, and the telephone hand sets18 are all in position onthe respective telephone sets, a D.-C. voltage,for example of about 30 volts exists. between two 'voice channel lines28 and '30 .(Figure' 2). The manner in which this voltage is providedwill be explained subsequently, The leads 2 8 and 30, along with fourother lines 32, 34,36 and; 38 forrn the interconnecting cable 8 and areconnected toeach one of the relay control units 6, and the telephone2,in exactly the same manner. The components of 'Figure 2 represent theapparatus in each one of the remotely-positioned ofices, that is, itrepresents diagrammatically the electrical apparatus contained in eachrelay control unit 6 and telephone set 2.

When the hand set 18 is removed from its cradle, indicateddiagrammatically at 40 in Figure 2, cradle switch contacts 42" areclosed, completing a circuit from the voice-channel line 28 through anactuating winding 44 of a privacy relay, generally indicated at 46, tothe other voice-channel line 30; thus impressing the D.-C. voltagereferred-to above upon this relay.

Bnergization ofthe privacy relay 46 closes its contacts 48,'com'pletinga circuit from line 30 through relay contacts 48, a microphone 50contained in the hand set 18, and an inductor 52, and the cradle switchcontacts 42 to the line '28.

As will be explained later, the voltage applied to lines 28*and 30 ispoorly regulated, as by connecting a substantialimpedance in series withit, so that a relatively large drop in the D.-C. voltage occurs when aload is impressed onthe lines by the actuation of the privacy relay 46.To this end, the resistance of the privacy relay winding 44 ispreferably high compared with the re- 'sistance; of the microphone50'and the inductor 52. Thus, for example, the winding 44 may have aD.-C. resistance of the order off-500 ohms whereas the inductor 52 mayhave a resistance of the order of 20 ohms, and the microphone may have aresistance of the order of 50 ohms.

Thus,- when the relay is actuated, the load impressed on the leads 28and 30 by the connection of the microphone 50 and the inductor 52 acrossthese leads is increasedsubstantially. This increased load causes amarked reduction in the voltage appearing between leads 28 and 30.Forexample, if an initial potential of 30. volts is'provided, thisvoltage may drop to a value of about-2 volts upon the energization ofthe privacy relay 46.

This relay 46 is arranged so that the lower voltage is-suflicient toholdthe relay in closed position but would be insufiicient to actuate therelay to its closed position. Relays-having the requisitecharacteristics are well-known, the large ditferential between closingand holding voltage being, most-readily obtained by utilizing a relayhaving a. relativelylarge gap between the armature and the iron coreofthe relay.

The. leads 28 and 30 are common to all of the other relay control units6 in other'ofiices and it is thus apparent that when any one of therelays 46 has been actuated, the voltagebetween lines 28 and 30immediately drops to a value much lower than its initial value and whichis insufficient to permit operation of any of the other privacy relays46lwhen the'associated hand set 18 is lifted."

The. clutch switch referred to above and carried by the. handset 18..isillustrated diagrammatically at 54in Figure 2. This switch is arrangedto start and stop the dictating machine 14 so-thatthe dictated materialwill be recorded in'the usualmanner.

Closing the clutch switch 54 completesa circuit which may be. tracedfroma negative-voltage supply line 32 (from the negative terminal of apower supply to be described-later), through contacts 56 of'theprivacy'relay 46,. an arm 58 and a. contact point- 60 of the markingswitch 120, the clutch switch 54, an actuating :wiuding 62 t t '4 of areceiverrelay, generally rent-limiting resistor 66 tothepositive-voltagesupply line later.

this lamp, and'the, corresponding lamp at each of the-dice tatingstations, is illuminated whenever any one of the 1 privacy relays isclosed.

Energization of the receiver, relay 64. closes itscontacts 6.8andconnects the receiver 70, of the handset 18, across an inductor 72, oneend of which is connected i to one end of the inductor 52 and to a lead73 extending between one terminal of the microphone 50 and one terminalof the head phone 70; the opposite end of the, inductor 72-isconnected'through aninductor 74 and a condenser 76 to the otherterminalof the microphone 50.

The arrangement of the coupled inductors 52, 72, and Hand the condenser76 are well known and-commonly usedin the telephone art, and will not bedescribed in detail here other than to point out that this arrangement1.

attenuates the-sound reproduced by-the receiver 70 when the person isdictating, but which permits-substantially increased volume in thereceiver 70 when the sound is applied tothehand set from the lines 28and 30, as during play back.

It will be noted that-the receiver 70 is disconnected from the circuitsunless the privacy relay 46- and the receiver relay 64 are energized-sothat any possibility of listening-in from another of the dictatorstations is prevented.

When the clutch switch-54 is closed, energizing'the receiver relay 64,the negative voltage from line 32 is connected by means'of a lead 78 andreceiver relay contacts 80 tothe clutch-control line 36, Which controlsthe clutch-operating circuits as will be explained presently.

When the marking switch 20 is-actuated, moving the arm 58 intoengagement with a contact 82, the negative voltage of line 32 isconnected to the marking-control line 38' by a circuit which can betraced from line 32 through contacts 56 of the privacy relay 46, arm 58and contact 82 1 ofthe marking switch 20, and switch contacts 84, op-

eratedby'the cradle 40, to the marking-control line 38. This circuitisarranged, as will be explained presently, to actuate the correctionmarker, which isgenerally indicated at 86 on the dictating machine 14 inFigure 1.

When the play-back switch 24 is actuated, both the marking andclutch-controltcircuits are completed simultaneously and operate theplay-back mechanism. A first 1 circuit can, be traced from the negativesupply line 32 through contacts 56 of the privacy relay 46, contacts88 I'of'the play-back switch 24, and'through the cradle switch 1 contacts 84to the marking-control line 38'; thus applying the negative voltage ofline 32 to the line 38. Simultaneously, the clutch circuit is completedwhich can be traced from line 32 through the privacy relay contacts 56,contacts 90 of the play-back switch 24, actuatingwinding 62 of thereceiver relay 64, and through the currentlimiting resistor 66 to thepositive lead 34, thus energizing the receiver relay 64 and connectingthe negative :voltage of lead 32 through receiver relay contacts 80 tothe clutchcontrol line 36.

The operation of the system to this point can be summarized as follows:Whentheprivacy relay 46-is energized, by lifting the hand-set 18; fromthe cradle 40,;the D.-C. voltage on lines 28 and 30 is reduced tosuch anextent that no other privacy relay can be energized, and arelay-operating voltage is caused tobe appliedto lines 32 and 34. Whenthe clutch switch.54=is actuated, the negative supply lead 32 isconnected directly to the clutch-control 'line 36. When a correctionmark is to be made by actuating the switch20, the negative Voltage ofindicated at 64, and a curlead 32 is applied to the marking-control line38. When the play-back switch 24 is actuated both the clutch and markingcircuits are completed to apply the voltage from the negative supplyline 32 to the clutch-control line 36 and to the marking-control line38. Simultaneous presence of these two control voltages actuates theplay-back mechanism. This arrangement reduces the number of hues whichmust be connected between the central control unit 12 and the dictatorstations.

Figure 3 illustrates diagrammatically the electrical apparatus which iscontained in the central control unit 12 and which serves as the controlapparatus for from six to ten dictating stations all of which areconnected to the central control unit 12 of the dictating machine 14.

The voltage for operating the privacy relay 46 is provided by a powersupply indicated in block form at 92. Since poor voltage regulation is adesired feature of this circuit, the power supply 92 may include aconventional resistance-capacitance filter circuit. This filteringshould be such as to remove substantially all of the A.-C. ripple as thevoltage is applied to the same lines that carry the voice signals. Thepositive supply terminal 94 of the power supply is connected through alead 96, an actuating winding 98 of a holding relay, generally indicatedat 100, to the voice-channel line 28, which, when the cradle switchcontacts 42 are closed (Figure 2), is connected through the privacyrelay winding 44 to the other voicechannel line 38. This line 30 isconnected (Figure 3) through a winding 102 of a second holding relay,generally indicated at 104, and a lead 106, to the negative supplyterminal 108 of the power supply 92. When the privacy relay 46 isactuated, as explained above, placing a relatively low resistance loadbetween the lines 28 and 30, sufiieient D.-C. current flows through theholding relays 1130 and 104 to actuate them and close their respectivecontacts.

When the holding relay 100 is energized, the relayoperating voltage isapplied between leads 32 and 34 by a circuit which can be traced from apositive output terminal 110 of a power supply, indicated in block format 112, through a lead 114, and contacts 116 of the holding relay 100,to the positive supply line 34, which is connected, as shown in Figure2, to the actuating Winding 62 of the receiver relay 64. The negativeterminal 118 (Figure 3) of the power supply 112 is connected by a lead120 directly to the negative supply line 32, which as shown in Figure 2is connected to the marking, play-back and clutch-control circuits.Because the power supply 112 provides voltage for operating relays, itneed not have as complete filtering as the power supply 92, but itshould have good regulation.

The other holding relay 104 is provided with a set of contacts 122 whichcomplete the power circuit for a motor 124, shown in Figure 4, of thedictating machine 14. This circuit can be traced from a 115 volt A.- C.power main 126 (Figure 3) through a lead 128, the contacts 122 of theholding relay 194, a lead 138, to one terminal of the motor 124 shown inFigure 4. The other terminal of this motor is connected by a lead 132and a common supply lead 134 to the other alternating current supplymain 140 (Figure 3). Thus, whenever the hand set 18 is removed from itscradle, the holding relay 104 energizes the dictating machine motor 124.

The supply mains 126 and 140 are connected in the usual manner toenergize the power supplies 92 and 112, it being understood that asuitable main switch and fusing arrangement will be included, thesecomponents having been omitted from the showing in order to simplify thedrawings.

As explained above, when the clutch switch 54 (Figure 2) is actuated,the receiver relay 64 is energized and the negative voltage on line 32,from the negative terminal 118 of the relay power supply 112, isconnected to the clutch-control line 36. As shown in Figure 3, the line36 is connected by a lead 144 to one end of the-actuating winding 146 ofa clutch-operating relay, generally indicated at 148. The other end ofthe winding 146 is connected through the lead 114 to the positiveterminal of the power supply 112.

The clutch-operating relay 148 thus is energized closing its contacts150 and completing a clutch-actuating circuit that can be traced fromthe positive terminal 152 (Figure 4) of a power supply, indicateddiagrammatically at 154, which is included as a portion of aconventional type dictating-machine amplifier assembly, indicatedgenerally in block form at 156, through a lead 158, the normallyclosedcontacts (Figure 3) of a limit relay, generally indicated at 162,contacts 150 of the clutch-operating relay 148, a lead 164 (Figure 4), acurrent-limiting resistor 168, an actuating winding of asolenoid-operated clutch, indicated diagrammatically at 172, and a lead174 to the negative terminal 176 of the power supply 154, which isconnected also directly to the supply main 140.

When the clutch-operating solenoid 170 is energized, the clutch 172couples the motor 124 mechanically to the driving mandrel of thedictating machine 14 in the usual manner.

When the marking switch 20 (Figure 2) is actuated, the negative voltageon line 32, from the relay power supply 112, is connected to themarking-control line 38 as explained above.

The line 38 (Figure 3) is connected by a lead 178 to one terminal of anactuating winding 180 of a delaying relay, generally indicated at 182,the other terminal of which is connected by the lead 114 to the positiveterminal 110 of the relay power supply 112.

When the winding 180 of the delaying relay is energized its contacts 184are closed, completing a circuit from the negative terminal 118 of thepower supply 112 through the lead 120, delaying relay contacts 184, anactuating winding 186 of a marking relay, generally indicated at 188,and the lead 114 to the positive terminal 110 of the power supply 112.

Thus, when the delaying relay 182 is energized, it causes energizationof the marking relay 188, but a short time delay is introduced becauseof the time required for actuation of the delaying relay. The reason forthis time delay will be made clear presently.

If the marking switch 20 (Figure 2) were closed for a very shortinterval of time, the marking relay 188 might not remain closed longenough to insure that a good correction mark would be produced. In orderto obviate this difliculty, a condenser 190, for example, ofelectrolytic type and having a capacity of 180 microfarads, is arrangedto discharge through the energizing winding 180 of the delaying relay182 each time the marking switch 20 is actuated, thus insuring that themarking relay will stay closed long enough to make a good mark.

One terminal of the condenser 190 is connected through the lead 114directly to the positive terminal 110 of the power supply 112, and itsother terminal is connected through a pair of normally-closed contacts192 of the clutch relay 148 and arm 194 and contact 196 of the delayingrelay 182 to the negative terminal 118 of the power supply 112. Thus,the condenser 190 normally is charged to the voltage delivered by thepower supply 112. When the delaying relay 182 is energized, its contactarm 194 is switched from contact 196 to a contact 198 that is connectedthrough the delaying relay winding 180 to the positive terminal 110 ofthe power supply 112. The condenser 190 then discharges through thewinding 18! maintaining the energization of the delaying and markingrelays during this time which is suflicient to produce a clearcorrection mark even if the marking switch is closed only for a moment.

The correction marks for the guidance of the secretary are, as usual,made upon the top sheet of the pad 22v (Figure-4) on the fron-t,o..thedictating machine 14. The; marking-mechanism-is actuated by apivotally-supported bail 202. which-is. arranged to move a lever 204 ofa conventional; marking, device 206, the bail 202 being operated by asolenoid, generally indicated at 208. This entiremarking assemblyisindicated diagrammatically, it being understood that anydesiredapparatus can be used to. produce the marks.

Power for operatingthe marking solenoid 208 is provided byarectifier-filter circuit (Figure 3) including a series resistor 210, adry disk-type rectifier 212 and a condenser 214.

The alternating current supply main 126 is connected through theresistor 210, for example of about300 ohms, and the half-wave rectifier212 to one terminal of the condenser 214, the other terminal of which isconnected directly to the other supply main 140. When there is no loadupon this circuit, the condenser 214 is charged to the peak'voltage ofthe alternating current source. When the marking relay 188 is energized,the condenser 214 is connected to; the solenoid 208 ad dischargesquickly through the solenoid, The condenser 214 is relatively large, forexample, of 100 or 200 rnicrofarads, so that the-surge of currentthrough the marking solenoid is adequate to, operate the marking device,but the voltage drop across the series resistor 218,.under loadconditions, prevents continued efl'ective energization of the markingsolenoid 208. Thus, the marking device produces a single indicating markeach time the marking switch 20 is clos d, but no further marks areproduced even if the markingswitch20 remains in the closed position.

The energizing circuit for the marking solenoid 208 can be traced fromthe supply main 128 through the voltage-dropping. resistor 210, therectifier 212, a lead 216, normally-closed contacts 218 of theclutch-operating relay- 148, contacts 220 of the marking relay 188, alead 222, the solenoid 208 (Figure 4), and lead 134 to the othersupply-main 140.

As was explained in connection withFigure 2, when the play-back switch24 is actuated, the negative voltage of line 32, from the power supply112, is connected to the clutch-control line 36 and also to themarking-control line 38; The play-back switch 24 thus causesenergization of the clutch-operating relay 148' and also. of ,themarking relay 188, through the delaying relay as described above.Simultaneous energization of the clutch-operating and marking relaysenergizes the play-back circuits of the dictating machine 14.

The connection between line 32 and the line 36, caused by closing ,theplay-back switch 24, completes a circuit that can be traced from thenegative terminal 1180f the relay-power supply 112 (Figure 3-) throughthe lead 120, line 32, line 36 (by means of the circuits shown in Figure2), lead 144, the actuating winding 146 of the clutchoperating relay148, and the lead 114 to the positive terminal 110 of the power supply112. This energizes the clutch-operatingcircuits as describedpreviously, starting rotation of the record-driving mechanism of thedictating machine 14.

The other connection, alsocaused by the closing of the play-back switchcontacts, between the negative supply line, 32 and the marking;controlline 38 energizes the delaying relay 182 by a circuit that can be tracedfrom the negative terminal 118 .of the relay power supply 112 through alead 120, the line 32, the line 38 (through the circuits, of Figure 2),the lead 178, the actuating winding 180 ofthe delaying relay 182, andthe lead 114 to the positive terminal110 of the relay power supply 112.As previously explained, the closing of the delaying relay contacts 184completes the circuit energizing the marking relay. 188.

Although the closing of play-back switch contacts causessimultaneousenergization of the clutch-operating and marking circuits, theclutch-operating relay 148 is actuated before the marking relay188.because of the time delay interval introduced by the delayingrelay182. Under these circumstances, the marking relay 188 does not causeenergization of the marking solenoid 208 (Figure4) because theclutch-operating relayopens its contacts 218 which are connected inseries with the circuit by which the marking. solenoid 208 is energized.This does not interfere with the normal operation of the marking circuitbecause the correction marks are. made only when the clutch-operatingrelay is de-energized.

When the clutchroperating and marking relays 148' and 188 are bothenergized, a circuit is completed that can:

be traced from the negative terminal 176 of the power supply 154 (Figure4)., in the dictating machine 14,

through the lead 134, clutch-operating relaycontacts. 226 t (Figure 3),marking relay contacts 228, a lead 230, an

actuating winding 232 (Figure 4) of a solenoid-operated record-reproduceswitch, diagrammatically and generally indicated at 234, acurrent-limiting resistor 236, the. lead 164, the clutch-operating relaycontacts 150 (Figure 3)., the normally-closed limit relay contacts 160,and the lead 158 to the positive terminal 152 of the power supply 154(Figure 4).

The switch 234 is arranged in conventional manner to shift theelectronic circuits from the recording .to the reproducing arrangementand to disconnect the recording head 238 and to connect the reproducinghead 240 which is arranged to track the record, in thisexampleillustrated as a flexible belt at 242, a short distance behind therecording head 238 so as to play back the most recently recordedmateriaL It is to be understood that this portion of the apparatus isillustrated only diagrammatically for the reason that any desiredplay-back mechanism can. be used, for example, :one in which a ratchetor other mechanism is provided to backspace the reproducing head.

During play back, both the marking relay 188 and the v clutch-operatingrelay 148 are energized as described above. At the end of the play-backoperation, if the clutch operating relay 148 were de-energized beforethe marking relay 188,. the marking circuits would be efiee tivethrough, the clutch relay contacts 218 to cause an unwanted correctionmark to be made. This possibility is obviated by the provision of aholding circuit for the clutchroperating relay 148 that maintains theenergization of the clutch relay until the marking relay 188has beende-energized.

This holding circuit can be traced from the negative terminal 118 of thepower supply 112 through the lead 120, clutch-operating relay contacts243, marking relay contacts 244, a lead 245, the lead 144, the winding146 of the clutch-operating relay 148, and the lead 114 to the positiveterminal 110 of the power supply 112. Energizareceiver 70' (Figure 2)indicating that a predetermined.

from the operator, it is particularly important that the operator beinformed when the recording head is nearing the end of the record. Thepresent system provides for two signals, a first low-level audible tonein the telephone amount of recording time remains on the record,for'example, one minute. At the end of the recording time,

a high-level audio signal is reproduced by the receiver 70 i and therecording mechanism is switched off simultaneously.

As is indicated diagrammatically in Figure 4, an arm 246 supported bythe reproducing-recording head carriage 247 is arranged to open thecontacts of a warning switch 248 as the carriage 247 nears the end ofthe usable.

recording area of the record.

This switch 248 controls the energization of an alterhating-currentwarning relay, generally indicated at 250- in Figure 3, through acircuit that can be traced from the 9 alternating current supply main140through the lead 134 (Figure 4), the warning switch 248, a lead 252(Figure 3), an actuating winding 254 of the warning relay 250, contacts256 of the limit relay 162, and leads 258 and 128 to the supply main126.

The contacts of the warning switch 248 are normally closed so that thewarning relay 250 is energized. As the carriage 247 approaches the endof the record, the switch 248 is actuated to its open position,de-energizing the warning relay 250.

The audible warning signal is produced by a conventional type buzzer,generally indicated at 260, which is energized, when the warning relay250 is de-energized by a circuit that can be traced from the negativeterminal 118 of the relay power supply 112 through warning relaycontacts 262, buzzer contacts 264, a buzzer-actuating Winding 266, alead 268, and the lead 114 to the positive terminal 110 of the powersupply 112.

The audio fiequency signal developed across the winding 266 of thebuzzer 260 is coupled to the audio leads 28 and 30 by a balanced circuitthat can be traced from one end of the winding 266 through a couplingcondenser 270, warning relay contacts 272, and a lead 274 to thevoice-channel line 28. The other portion of this circuit can be tracedfrom the opposite end of the buzzer winding 266 through a couplingcondenser 276, warning relay contacts 278, and a lead 280 to the line30.

The Warning-signal coupling condensers 270 and 276 are selected withsuch capacities that the audio signal is only faintly heard in thereceiver 70 and of such low amplitude that it does not interfere withthe normal dictating procedures. Each of these condensers may have, forexample, a capacity of 100 micromicrofarads. The warning signal may becontinuous for the remainder of the recording time or it may provideonly a momentary signal, depending upon whether the arm 246 is arrangedto retain the warning switch 248 in open position.

When the carriage 247 has moved to a position where substantially theentire recording area of the record has been used, the arm 246 strikes alimit switch 281 and de-energizes the limit relay 162. The circuit bywhich the limit relay 162 is normally energized can be traced from thepower main 140 through the lead 134, the limit switch 281, a lead 282,holding relay contacts 283 (Figure 3), a lead 284, an actuating winding286 of the limit relay 162, and the leads 258 and 128 to the othersupply main 126.

When the arm 246 strikes the limit switch 281, interrupting thiscircuit, the limit relay 162 is de-energized closing its contacts 288and 290 and providing increased coupling between the opposite ends,respectively, of the buzzer winding 266 and the leads 28 and through twoadditional coupling condensers 292 and 294. These condensers 292 and 294are of substantially greater capacity than the condensers 270 and 276and, for example, may have a capacity of the order of two thousandmicromicrofarads. This increased coupling produces a relatively loudwarning signal in the receiver 70 indicating that no further recordingis possible until the record 242 has been replaced.

When the limit relay 162 is de-energized, its contacts 160, which are inthe energizing circuit for the clutch 172, are opened, thus preventingfurther energization of the clutch.

The signal lamps 26 (Figures 1 and 2) at each dictating station areenergized through the holding relay contacts 116 (Figure 3) whenever anyone of the dictating stations is in use. This lamp 26 is energized alsowhenever the record 242 is filled, that is, whenever the limit relay 162is de-energized, irrespective of whether any dictating station is inuse. This is accomplished by the limit relay contacts 296, which areconnected in parallel with the holding relay contacts 116.

The audio signals impressed on the. balanced line formed by the leads 28and 30 during dictation, develop corresponding signal voltages acrossthe resistances offered by the windings 98 and 102 of the holding relaysand 104.

These voltages are transferred to the amplifier circuits of thedictating machine 14 by an isolating and impedance matching networkincluding two condensers 298 and 300 which are connected, respectively,to the leads 28 and 30 and to the opposite terminals of a primarywinding 302 of an audio transformer 304, the secondary winding 306 ofwhich is connected to the primary winding 308 of another audiotransformer 310. The secondary winding 312 of the transformer 310 isconnected by a shielded cable 314 to the amplifier circuits of thedictating machine.

It will be noted that the lines 28 and 30 are balanced and terminatedsymmetrically at each end so that the lines can be placed near telephoneor other interoflice Wires without picking up objectionable cross-talkor hum,

Two holding relays 100 and 104 have been illustrated although a singlerelay can be used provided a corresponding impedance is used to replacethe relay winding. These relays have a resistance, in this example, ofabout 500 ohms so that they provide an adequate signal load im- Hpedance and produce the desired poor voltage regulation characteristics.

From the foregoing, it will be observed that the dictating systemembodying the following claimed invention is well adapted for theattainment of the ends and objects hereinbefore set forth and that itcan be installed and maintained easily and economically.

What is claimed is:

1. In an ofiice-type dictating system wherein recording apparatus isconnected to a plurality of remotely-positioned dictating stations,apparatus comprising a plurality of microphones at least one of which ispositioned at each of said remote stations, a line extending betweensaid recording apparatus and each of said remote stations, a pluralityof relay means, a plurality of switch means each of which is associatedwith one of said relay means to be operated upon actuation of itsassociated relay means and each of which is coupled to one of saidmicrophones and to said line and each of which, upon actuation of itsassociated relay means, connects its associated microphone through saidline to said recording apparatus, a voltage source for actuating saidrelay means, interconnecting means coupling said voltage source to eachof said relay means, and means responsive to the actuation of any one ofsaid relay means for reducing the operating voltage applied through saidinterconnecting means to each of said relays from said source below theminimum value effective to initiate actuation of any one of said relaymeans.

2. In an oflice-type dictating system wherein recording apparatuslocated at a central station is connected to a plurality ofremotely-positioned dictating stations, apparatus comprising a pluralityof signal transducing devices, at least one of which is positioned ateach of said remote stations, a connection extending between saidrecording apparatus and each of said remote stations, a plurality ofrelay means, all requiring substantially the same predetermined minimumoperating voltage, a plurality of switch means each of which isassociatedwith one of said relay means and operated thereby each of saidswitch means being coupled to one of said signal transducing devices andto said connection and operated upon actuation of its associated relaymeans to connect its associated signal transducing device to saidconnection to said recording apparatus, a source of voltage at leastequal to said minimum operating voltage, interconnecting means couplingsaid voltage source to each of said relay means, effectively highimpedance in circuit with said voltage source and said interconnectingmeans and efiectively lower impedance associated with each of saidsignal transducing means and responsive to the operation of any 11, 7one :of said relaymeans to be applied to saidinterconnecting means forreducing the operating voltage applied to each of said relay means fromsaid source below the minimum value efiective to operate any one of saidrelay means.

3. Inanoflice-type dictating system wherein recording apparatus locatedat a central station is connected to a plurality of remotely-positioneddictating stations, apparatus comprising a plurality of microphones oneof which is positioned at each of said remote stations, a connectionbetween said recording apparatus at the central station and each ofsaid' remote stations, a plurality of relay means, all requiringsubstantially the same predetermined minimum operating voltage, each ofsaid relay means being'connected between one of said microphones and'said connection and arranged upon actuation toconnectits associatedmicrophone through said connection tosaid"record.i'ng apparatus,a-source of voltage at least equal to said minimum operating voltage,interconnecting means coupling said voltage source to each of said relaymeans, and impedance means connected in series with said voltage sourceand having impedance to reduce the voltage applied to each of said relaymeans from said voltage source to a value below said minimum operatingvoltage.

4. In an ofiice-type dictating system wherein the sound recordingapparatus is located at a central station and connected to a pluralityof remotely-positioned dictating stations; apparatus comprising aplurality of telephones each having a hand set and microphone, one ofsaid telephones being positioned at each of said remote stations, aplurality of privacy relays having open and closed conditions ofoperation, all of said relays requiring substantially the samepredetermined minimum operating voltage for causing their operation fromopen to closed condition and requiring substantially the same lesservoltage for holding them in the closed condition, each of said relaysbeing connected in circuit between one of said microphones and saidrecording apparatus and arranged in closed condition to connect itsassociated microphone to said recording apparatus, a source of voltagegreater than said minimum operating voltage, a plurality of switcheseach positioned in one of said telephones and responsive to the liftingof the associated handset, to connect the associated relay to saidvoltage source, and means responsive to the operation of any one of saidrelays into closed condition for reducing the operating voltage appliedto each of said relays from said source to, a value below the minimumoperating value and above the holding value for holding said one relaymeans, in its actuated. condition while preventing the actuation of anyother of said relays.

5. An ofiice-type dictating system comprising a plurality, of separatedictating stations each including electro-acoustical transducer means, acentral sound recording station positioned remotely from said dictatingstation including a. record, a recording head for impressing soundsignals on said record, and a recording amplifier connected to saidrecording head and supplying amplified. sound signals thereto, abalanced signal-transmission line extending between each of saidtransducers and the recording amplifier, an audio signal-generatorpositio'ned'at said central station and having a pair of outputterminals, a pair of coupling condensers each of substantially equalcapacitance, and a pair of switch means, each of said'switch means beingin circuit with one of said output terminals, one of said condensers,and one side of said transmission line to connect one of said condensersbetween each of said terminals andthe trans mission line, said switchmeans being responsive to the positioning of the recording head near theend of the recording area on said record.

6; In anoflice-type remote-control dictating system whereinsoundrecording apparatus is located at a central station and connectedto aplurality of remotely-positioned record, a-recording head, and anamplifier connected to 7 said head for supplying amplified electricalsignals there-n dictating stations, signalling apparatus comprisingsound recording apparatus positioned at said central station'and.

having first and secondconditionsofi operation; an audio frequencygenerator located at saidcentral station'and arranged to produce anelectrical-signal 'of audioifi'equency, a pair of output :terminals-onsaidgenerator, a 7

transmission line extending from said sound recording apparatus tosaidremotely-positioned stations, first and,

second pairs of couplingcondensers, the condensers of said first pairbeing of substantially equal and relatively small capacitanceand thecondensers'of said second pair being of substantially equal andrelatively large capaci= tance, a first pair ofswitch elementsunder'the'control of said sound recording apparatus, each of said switchelements of said first pair being in circuitwith oneof said outputterminal, one of said condensersof said-first pair and one side of saidtransmission line toconnect said first pair of condensers between saidterminals and'said transmission line When said recorder is in saidfirst-condition of operation, and a second pair-of switch elements underthe control of said sound recording apparatus,

each of said switchelements of said second pair being in circuit withone of said output terminals, one of said condensers of said second'pairand one side of said transmission line to connect said second pair ofcondensers between said terminals and said transmission line when saidrecorder is in'said second condition of operation;

7. An ofiice-type dictating system comprising a plurality of separatedictator stations each including a transmitter and a receiver,v acentral sound recording station: positioned remotely from said dictatorstations: includinga to, a balanced signal-transmission line extendingbetween the transmitter and. receiver at each of said dictator sta tionsand said amplifier, an audio signal; generaton positioned at saidcentral station, a pair of outpuuterminals on said generator, twopairsof coupling condensers, the

condensers of each of said pairs'beingof substantially equal capacitanceand the condensers of Voneof saidpairs being of'substantially greatercapacitance than thoseof the other pair, switch means for connecting oneofthe condensers of each pair betweerr one of said output terminals andthetransmission line and the: other condenser of each pair between theother output terminal; and the, transmission line, said switch meansbeing responsive-to v recording area of said record for connecting theother pair of condensers between said terminals and the transmissionline for transmitting to said receivers an-audio signal of relativelyincreased energy.

8. In an oifice-type central-station dictating system trol elements fromreleased to actuated position, aclutch-g circuit, a clutchrelay havingsecond circuit control-elements with released and actuated positions andcontrolled by said clutch circuit to change said second circuit controlelements from released to actuated position, a play back mechanism incircuit with said first and second cir'- cuit control elements so :as tobe under the cont-roli'of both of said relays to be energized whensaidfirs t-'andi second circuit control elements of eachof said relaysis in its actuated position,-and a manual play-back control locatedatsaid dictating station, switch-meansd'n' circuit with both-said mark-ingand clutch-circuits and und'erthe,

stations so that communication control of said manual play-back control,whereby operation of said manual play-back switch energizes both saidmarking and clutch circuits to place said first and second circuitcontrol elements of said marking and clutch relays in actuated positionwhereby said play-back circuit is energized.

9. In an office-type central-station dictating system wherein soundrecording and reproducing apparatus located at a central station isconnected to a remotelypositioned dictating station, apparatuscomprising a marking relay having first circuit control elements withreleased and actuatedpositions and controlled by said circuit to changesaid first-circuit control elements from released to actuated position,a clutch circuit, a clutch relay having second circuit control elementswith released and actuated positions and controlled by said clutchcircuit to change said second circuit control elements from released toactuated position, a play-back mechanism in circuit with said first andsecond circuit control elements so as to be under the control of bothsaid relays to be energized when said first and second control elementsof each of said relays is in its actuated position, a manual playbackcontrol located at said dictating station, switch means in circuit withboth said marking and clutch circuits and under the control of saidmanual play-back control, whereby operation of said manual play-backswitch energizes both said marking and clutch circuits to place saidfirst and second circuit control elements of said marking and clutchrelays in actuated position to energize said play-back circuit,time-delay means connected to said marking relay for preventing theactuation of said marking relay until said clutch relay is in itsactuating position, and a holding circuit arranged to maintain theclutch relay in actuated position until the marking relay has returnedto its released position.

10. Apparatus as claimed in claim 9 wherein said time delay meanscomprises a relay having contacts arranged to energize said markingrelay.

11. In an office-type central-station dictating system wherein soundrecording and reproducing apparatus located at a central station isconnected to a plurality of remotely-positioned dictating stations,apparatus comprising a play-back circuit arranged to reproduce saidrecorded sound, a marking circuit including a marking relay havingreleased and actuated conditions, a pair of relay contacts on saidmarking relay and forming a conductive path therebetween when said relayis in its actuated condition, a clutch circuit including a clutch relayhaving released and actuated conditions, a pair of relay contacts onsaid clutch relay and forming a conductive path therebetween when saidclutch relay is in its actuated condition, and means for energizing saidmarking and clutch relays to place them in their actuated positions,means under the control of said relays arranged to energize saidplay-back circuit when both of said relays are in their actuatedconditions, a holding circuit arranged to energize the clutch relay tohold it in actuated condition, said holding circuit being completed byconductive paths including said relay and clutch contacts connected inseries, said holding circuit being independent of the mar 'ng and clutchcontrol circuits.

12. An office-type dictating system as claimed in claim 1 and whereineach tively small impedance and said voltage source has an efiectivelylarge impedance in circuit therewith, and wherein each of said switchmeans when operated by its associated relay means connects itsassociated microphone in circuit with said interconnecting means,whereby the low impedance of said microphone reduces the operatingvoltage on said interconnecting means below the value efiec-tive toinitiate actuation of any one of said relay means.

13. In an ofiice-type dictating system wherein a recording machine isconnected to a plurality of remote may be made from any of saidmicrophones has an eflecbeing connected to said first line,

one of said stations to said recording machine and wherein each stationincludes sound transducing means through which said communication ismade, apparatus enabling communication to be made through thetransducing means at any one of said stations and for preventingsimultaneous communication to be made with said recording machinethrough the transducing means at any other station, comprising a firstline extending between said remote stations, a voltage source, saidvoltage source a second line extending from said recording machine toall of said stations, a plurality of relay means each operativelyassociated with one of said stations and each including circ 't controlmeans which operate upon actuation of the relay means, each of saidcircuit control means being connected between said second line and itsassociated sound transducing means at the associated station, to coupleits associated sound transducing means to said second line uponactuation of the relay means, a plurality of controls, each controlbeing operatively related to one of said stations and being in circuitwith said first line and the relay means at the associated station,whereby operation of any one, of said controls actuates the associatedrelay means to operate its circuit control means to couple theassociated sound transducing means to the second line, and meansresponsive to the actuation of any one of said relays for reducing theoperating voltage on said first line below the minimum value effectiveto initiate actuation of any one of said relay means.

14. An otfice-type dictating system as claimed in claim 13 and whereinsaid first and second lines comprise a voice channel connected to saidrecording machine, said relay means are privacy relays, the windings ofsaid privacy relays have a relatively high impedance, all of saidprivacy relays require substantially the same predetermined minimumoperating voltage for causing their operation from open to closedcondition and require substantially the same lesser voltage for holdingthem in the closed condition, and said voltage source has a value atleast as high as said minimum operating voltage but has poor regulation,said voltage source is connected between said lines of said voicechannel, each of said controls is a manually-operable switch in circuitbetween one of said lines and one side of the winding of its associatedprivacy relay, with the other side of said'winding connected to theother line, each of said circuit control means is a switch in theprivacy relay, each of said privacy relay switches is connected inseries with said sound transducing means from one to the other of saidlines, and the means for reducing the operating voltage is a relativelylow impedance path through any one of said sound transducing means whenits privacy relay switch is closed, whereby when one of said privacyrelays is actuated, said sound transducing means is connected to thevoice channel and the operating voltage on said voice channel is reducedto a value below the minimum operating value and above the holdingvalue, thus holding said one relay in its actuated condition whilepreventing the actuation of any other of said privacy relays.

15. in an oflice type dictating system wherein a recording machine at acentral station is connected to a plurality of remote stations so thatcommunication may be made from any one of said remote stations to saidrecording machine and wherein each remote station includes soundtransducing means through which said communication is made, apparatusenabling communication to be made through the transducing means at anyone of said stations and for preventing simultaneous communication to bemadewith said recording machine through the transducing means at anyother station comprising: a voice channel connected to said recordingmachine, a plurality of relay means, all requiring substantially thesame predetermined minimum voltage to initiate actuation, each of saidrelay means controlling a switch connected in circuit with one of saidsound transducing means and to reduce the voltage applied'firom saidsource to each of'said relay means. below the mini'mum'value efl'ectivetoinitiate actuation of any one of said relay means.

16. 'A dictating system comprising a plurality of separate dictatorstations, each including a pair of output terminals, a sound transducer,first relay means includof said first relay means to connect said soundtransducer to its respective output terminals.

17. A dictating system as claimed in claim 16 and wherein each of saidfirst relay chine; a plurality of remote including a cuit'meansoperators stations each transducer and an on-ofl station switch; cir-1nclud1ng branch circuits leading from said remote stations when closed;respective relays for-said remotestations' conf6 v nected in therespective branchcircuits for operation by said potential source" as therespective station switches are closed; each of said relays havinga".voltagegcharacteristic' such thatit is operable by the.opencircuit'line voltage existing insaid branch circuits when the firstof said circuits is closed and such that it is inoperable by theline'voltages' at the remote sta one of said station switchesis alreadyclosed; and switch means in each relay for connecting the respectivetransducer to said machine as the relay is operated.

20. In aremotely-controlled multistation phonographic system including asource of potential: the combination of an attendants station includinga phonographic machine; a plurality of remote operators stations eachincluding a transducer and an on-ofi station switch; circuit meansincluding branchcommunication circuits leading from said remotestationsrespectively for connecting any selected one'of said transducersto said machine via the respective station switch and branch circuitwhen that station switchfis in on position; means connecting saidpotential source to said circuit means to'supply.

energizing potential to each of saidvbranch circuits; a relay at each ofsaid remote stationshaving a coilfcom nected for energization by saidpotential source via the respective branch circuit and station switchwhen the station switch is in on? position; means connected. to to causea substantial drop in pow connected in circuit; each relay switchmeansconnected in the respective branch the respective transducerthereto when the. relay is operated.

21. In a remotely-controlled.multistation phonographic systemincluding aD.r-C. source of potential: the combi-, nation of an attendants stationincluding a phonographic remote operators stations each including atransducer and a station switch'movable into on and off positions; meansconnected to said poany one of said station switches" to onposition'for. activating said phonographic machine for use; a stationconditioning relay at each remote station normally in. a stationdisabling position and effective when 'operatedto control circuit tochange said second circuit elements from ed to on position, afunction-operating mechanism in circu t with said first and secondcircuit elements so, as

connecting a to be under the control of both of said relays to beenergized when said first and second circuit elements of each of saidrelays are in their on positions, a manually-operable device located atsaid dictating station, and first and second switch means in circuitwith said first and second control circuits respectively, both of saidswitch means being concurrently actuable by said manually-operabledevice whereby operation of said manually-operable device simultaneouslyswitches both said control circuits to place said first and secondcircuit elements of said relays in their on positions so that saidfunction-operating mechanism is energized.

23. Apparatus as claimed in claim 22, including time delay means forsaid first function relay for preventing the actuation of said firstcircuit elements to their on position until after said second circuitelements have been placed in their on position.

24. Apparatus as claimed in claim 22, including a holding circuitarranged to maintain said second circuit elements in their on positionuntil said first circuit elements have returned to their oil position.

25. A remotely-operated dictation system which includescentrally-located recording and control equipment wherein a recordinghead is arranged for relative travelling movement with respect to amoving record, apparatus comprising, in combination, a plurality ofremote dictators instruments each including a microphone and an on-ofiswitch, circuit means for connecting any one of said instruments to saidrecording and control equipment, said circuit means being completed whenthe on-otl switch at said one instrument has been placed in on position,privacy switch means at each of said instruments and movable intoeflective and ineffective positions for rendering inoperative andoperative the respective remote instruments, a privacy relay at each ofsaid instruments for controlling said privacy switch means, the windingsof said privacy relays being connected to said circuit means to beenergized by current flowing therethrough, a source of energizingpotential at said recording and control equipment and connected to saidcircuit means for transmitting current to said privacy relays when saidcircuit means has been completed in response to the operation of theon-ofi switch at one of said instruments to its on position, and controlmeans associated with said circuit means and operable in response to thecompletion of said circuit means when the on-otf switch at oneinstrument has been placed in on position, said control means beingarranged to control the activation of said privacy relays so that theprivacy switch means at said one instrument is conditioned inineffective position and the privacy switch means at all otherinstruments are conditioned in eifective position, whereby the dictatorfirst to operate his on-ofi switch has an exclusive channel through saidcircuit means to said recording and control equipment.

26. In a remotely-controlled multistation phonographic system, thecombination of: an attendants station including a phonographic machine;a source of potential at said attendants station; a plurality of remoteoperators stations each including a transducer and an on-otf stationswitch; circuit means including branch circuits leading from said remotestations respectively for connecting said remote stations to saidattendants station when the respective station switch is in on position;means for supplying energizing potential to said branch circuits fromsaid potential source; respective disabling switches connected to saidcircuit means and movable into effective and ineffective positions forrendering inoperative and operative the respective remote stations;respective electrically-energizable devices for operating said disablingswitches and connected in the respective branch circuits for operationby current from said potential source; and means for controlling theflow of current to saidtelectrically-energizable devices in response toactuation of one of said on-oif switches to its on position, said meansbeing adapted to establish current flow to condition saidelectrically-energizable devices so as to render inoperative all of saidremote stations except the station associated with said one on-offswitch.

27. In a remotely-controlled multistation phonographic system, thecombination of: an attendants station including a phonographic machine;a source of potential at said attendants station; a plurality of remoteoperators stations each including a transducer and an on-ofi stationswitch control; circuit means including at least first and second pairsof lines leading from each of said remote stations respectively forconnecting said remote stations to said attendants station fortransmitting voice and control signals thereto when said circuit meanshas been completed by actuation of the respective station switchcontrol; means for supplying energizing potential from said potentialsource to said first pair of lines; respective disabling switchesconnected to said circuit means and movable into eifective andineffective positions for rendering inoperative and operative therespective remote stations; respective electrically-energizable devicesfor operating said disabling switches and connected to the respectiveones of said first pairs of lines for operation by said potential sourcewhen said circuit means has been completed; and means associated withsaid electrically-energizable devices and operable upon completion ofsaid circuit means in response to actuation of one of said on-ofistation switch controls, said means being operable to assure that saiddevices are conditioned to render inoperative all of said remotestations except the station corresponding to the on-ofI' station switchcontrol which is first actuated.

28. A remotely-operated dictation system which includescentrally-located recording and control equipment wherein a recordinghead is arranged for relative travelling movement with respect to amoving record, apparatus comprising, in combination, a plurality ofremote dictators instruments each including a microphone and an on-offswitch device, circuit means for connecting any one of said instrumentsto said recording and control equipment, said circuit means beingcompleted when the on-ofi? switch device at said one instrument has beenplaced in on position, privacy switch means at each of said instrumentsand movable into effective and inefiective positions for renderinginoperative and operative the respective remote instruments, relay meansconnected to said circuit means for controlling said privacy switchmeans, a source of energizing potential at said recording and controlequipment and connected to said circuit means for activating said relaymeans when the on-ofi switch device at one of said instruments has beenplaced in on position, and sequence control means for said relay meansarranged to assure that the privacy switch means at said one instrumentis conditioned in ineffective position while the privacy switch means atall other instruments are conditioned in effective position, whereby thedictator first to operate his on-off switch device has an exclusivechannel through said circuit means to said recording and controlequipment.

No references cited.

